Starting A 747 Isn't Like Turning A Key In The Ignition

KEN KAYE ON AVIATION

Ever wonder how to start up a Boeing 747, or any other jetliner for that matter?

You don't put a key in the ignition, give her some gas and fire that baby up.

The fact is, no keys are involved. Instead, you must go through a complicated series of procedures, flipping switches or pushing levers.

And that's just to unlock the airplane's entry door.

"What a lot of people don't realize is, once you get involved with anything larger than a small general aviation airplane, there is no key," said Steven Wallach, a former Eastern Airlines captain. "Anybody who can get in the door and knows the right sequence can just fly away."

Please note: This column is not intended to provide a how-to on jetliner theft. If anyone were stupid enough to have such a notion, he or she should know it's not easy to pawn a 400-ton piece of machinery that requires a football field's worth of space to park.

Rather, it is to show that airliners are extremely complicated, and to bring one to life, you must activate a number of systems in addition to the engines.

Let's pretend that our aircraft is on a ramp, away from any terminals, locked, dark and silent. You won't need keys because, in real life, 100 different crews may use this jet, and keys would be impractical.

To open the airplane's entry door, you must first find a compartment in the fuselage containing a mechanism to unlock and open the door. This is assuming you can find a tall stairway or some other way to reach that door, which may be up two stories high.

"There's no doorknob just sticking out there," said Wallach, of Fort Lauderdale, now an aviation consultant and an attorney who has represented airlines, aircraft manufacturers, pilots and airport operators, usually in air crash litigation.

Once inside the plane, you go into the cockpit and hit some more switches to provide electrical power and lights. But this step only allows you to see what you're doing.

To activate all electrical systems as well as others critical to the overall start-up, you must fire up the auxiliary power unit, or what's commonly known as the APU.

This is a mini-jet engine, usually positioned in the tail of an airplane. We'll bypass the specific start procedure, but suffice it to say it involves a checklist of procedures and more switches and levers.

Once it's humming, the APU provides the air that starts the other engines rolling. You then flick more switches and push more levers to initiate fuel flow and ignition in each engine.

But this isn't done haphazardly.

"This is done with precise timing and at a precise speed in order to effect a normal start," Wallach said. "If you were to introduce fuel too early, you're going to burn up the engine. If you do it too late, you may burn up the starter."

If you're wondering how a jet engine works, simply put, compressed air is moved into a chamber, where fuel is continuously ignited, something like a constant but controlled explosion. The expanded hot air is then pushed through a turbine and expelled out the back.

"It's the movement of the air out the back that causes the plane to go forward," Wallach said. "It's Newton's third law: For every action, there is an equal and opposite reaction."

Wallach said in principle, a jet engine works much differently from the piston engine of a car.

"Unlike a piston engine, where cylinders take turns firing, in a jet there is a ring of fire that fuel is sprayed through," Wallach said. "It's much less violent, in that respect, than an internal combustion engine."

Anyway, while each engine whines to life, you must monitor the oil pressure, engine operating temperature and turbine rotation speed gauges, among others.

And you thought your pilots were up there pumping the accelerator pedal, right?

On some newer jetliners, such as the Boeing 767 and the Airbus 340, you wouldn't have to work as hard. They essentially have one button that does much of the engine-start sequencing work.

OK. Now you have your jet purring like a kitten. Now what?

"Then all you have to do is know how to fly it," Wallach said.

If you have questions about airline operations or safety, Ken Kaye can be reached at kkaye@sun-sentinel.com.